Relay circuit



y 1939 J. M. WILSON- 2,167,227

RELAY CIRCUIT Filed June 2, 1958 CONTACTS OVERLAPPING ON TEMPERATURERISE ONLY w Fmg 2 Fig 11 Snventdr Jollmn MaWillson I BE attorneyPatented July 25, 1939 PATENT OFFICE RELAY CIRCUIT John M. Wilson,Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company,

Minneapolis, Minn., ware a corporation of Dela- Application June 2,1938, Serial No. 211,402

Claims.

The present invention relates to a relay circuit and more particularlyto one wherein provision is made for the relay moving to its deenergizedposition upon a relatively small reduction in voltage.

In certain types of control systems, it is highly desirable to have therelay drop out upon the voltage of the source of power decreasing arelatively small amount below the value at which the relay is pulled in.In the case of an oil burner" control system having electrical ignitionmeans, for example, a reduction in voltage during operation of theburner may cause the ignition means to become deenergized and yet stillpermit the motor to run. This is true inasmuch as in many systems, theignition means requires a much higher voltage forjoperation than do themotors of the systems. If the motor continues to run, oil will besupplied to the furnace, this oil being unignited. While means areusually provided for eventually deenergizing the system in the event ofcombustion failure, such means requires an appreciable time foroperation. If it is assured that the voltage is not sufficiently high tooperate the ignition, there is no need to delay the deenergization ofthe system for this period of time since it is assured that the burnerwill not again be placed in operation. It can readily be seen from theforegoing that it is highly desirable that the relay controlling the oilburner and ignition circuits be of a type which moves to its deenergizedposition upon a relatively small drop in voltage. It has been proposedin the past to connect a resistance in series with the relay coil uponenergization of the relay, this resistance serving to reduce the voltageapplied to the relay coil and hence to make it possible for the relay todrop out upon a relatively small reduction in line voltage. Thedisadvantage of such a resistance is that at the time that theresistance is connected in the circuit, the power factor is changed.This change in power factor may so disturb the flux flow in the corestructure of therelay that the relay drops out momentarily. Where, as itis desirable in the case of certain systems, the original energizingcircuit is interrupted at the moment the impedance is connectedin serieswith the relay coil, this dropping out of the relay instead of beingmomentary 50- will be. permanent, since the impedance is of such valuethat the relay cannot initially pull in with the impedance connected inseries therewith. q An object of the present invention is to providea,circuit arrangement for an electromagnetically operated device biasedto one position in which an impedance having the same power factor asthe electromagnetic operator is connected in series therewith uponenergization of the operator.

A further object of the invention is to provide a relay circuit in whichan impedance having the same power factor as the relay is connected inseries therewith upon energization of the relay.

.A further object is to provide such a relay circuit in which the relaycontrols a condition producing device and in which the connection of theimpedance is dependent both upon one of the relay switches and upon aswitch responsive to the condition produced by operation of said device.

A further object of the invention is to provide a relay circuitaccording to the previous object in which the condition responsiveswitch is effective to break the original energizing circuit to therelay as soon as the circuit including the impedance has beenestablished.

Other objects of the invention will be apparent from a consideration ofthe accompanying specification, claims and drawing, of which:

Figure 1 is a schematic view of an oil burner circuit including thenovel relay circuit oi? the present invention, and

Figure 2 is a slightly modified form of the relay circuit.

As indicated above, Figure 1 is a schematic view of an oil burnercontrol circuit incorporating the improved relay circuit. The oil burneris generally designated by the reference numeral I0 and comprises theusual nozzle II and the usual blower driven by a motor l2. The blower iseffective to force an atomized mixture of fuel through the nozzle ll.provided for the purpose of igniting the fuel issuing from the nozzle.This ignition means may be of any conventional type such as a highvoltage transformer connected to suitably spaced spark electrodes.

The energization of the oil burner and ignition means is controlled by arelay generally designated by the reference numeral l6. This relaycomprises a coil I1 which is operatively associated'with an armature l8connected to switch blades I9, 20, and 2t. Switch blades 69, 26, and 2|are biased to the right by any suitable means (not shown), but areadapted to bemoved, upon energization of the relay coil. i'i intoengagement with contacts 23, 2d, and 25, respectively.

An ignition means I4 is While the relay has been shown schematically asof a type comprising a solenoid coil through which a core is movable, itis to be understood that the relay can be of any conventionalelectromagnetic type wherein the reluctance of the magnetic circuit isdecreased upon the armature moving'to its energized position.

The energization of the relay I6 is controlled by a room thermostat 28.This room thermostat comprises a bimetallic element 21 to which issecured a composite contact arm 29. The contact arm 29 is adapted tosequentially engage contacts 38 and 3i. Upon a temperature fall, thecontact arm 29 is adapted to first engage contact and then to engagecontact 3|.

Also controlling the energization of relay I1 is a thermal safety switch35. This safety switch may be of the form shown in the patent to F. S.Denison No. 1,958,081, issued May 8, 1934. As shown in the drawingschematically, the switch comprises two switch blades 36 and 31, thelower one of which is pivotally mounted. The bimetallic element 38 whenin its cold position extends under switch blade 31 and holds the same incontact making position with switch blade 36. A heater 39 is locatedadjacent the bimetallic element 38 and serves when energized to heat theelement 38 causing the latter to warp to the right. It will be obviousthat if this heating is continued sufiiciently long, bimetallic element38 will be warped to the right sufficiently to permit switch blade 31 todrop away from switch blade 36.

A stack switch generally indicated by the reference numeral 48 isprovided for the purpose of indicating when combustion has taken place.This switch comprises a temperature responsive element (not shown) whichactuates a switch blade 4| through a slip friction connection. Theswitch blade 4| when in its cold position, engages a contact 42. Uponthe temperature responsive element of switch 48 being subjected to arise in stack temperature, the switch blade 4| is moved into engagementwith a contact 43. The assembly consisting of switch blade 4| andcontacts 42 and 43,is so designed that switch 3 blade 4| moves intoengagement with contact 43 before it moves out of engagement withcontact 42. Upon a temperature fall, switch blade 4| moves out ofengagement with contact 43 before it moves into engagement with contact42. In other words, the contacts are overlapping on temperature rise butnon-overlapping on temperature fall. The switch 48 may take the form ofthe switch disclosed in the patent to A. F. Erickson No. 1,969,974,issued January 2, 1934.

A choke coil is designated by the reference numeral 45. This choke coilis so designed as to have the same power factor as the relay coil |1when the armature of the relay is in its energized position. This chokecoil comprises the usual winding 46' and core 41 of magnetic material.

The step-down transformer 58 is provided for the purpose of supplyinglow voltage power for operation of the control portion of the system.This transformer comprises a line voltage primary 5| and a low voltagesecondary 52. The primary 5| is connected to line wires 53 and 54leading to any suitable source of power (not shown).

s'fperation of Figure 1 species The elements are shown in the system inthe position they occupy when the temperature to which thermostat 28 isresponsive is at or above the desired value. Upona drop in temperature,

the contact arm 29 first engages contact 38 and then contact 3|. Theengagement of arm 29 with contact 38 has no effect. As soon as itengages contact 3|, however, an energizing circuit is established torelay coil H as follows: from the right-hand terminal of secondary 52through conductor 56, contact- 38, contact arm 29, contact 3|,conductors 51 and 58, heating element 39, conductor 59, contact 42,contact blade 4|, conductor 68, relay coil l1, conductor 6|, switchblades 31 and 36, and conductor 62 to the other terminal of secondary52. The establishment of this circuit causes the energization of relaycoil |1 so that switch blades I9, 28, and 2| are moved into engagementwith contacts 23, 24, and 25, respectively.

The moving of switch blade 28 into engagement with contact 24 results inthe establishment of the following holding circuit to relay coil l1:from the right-hand terminal of secondary 52 through conductor 56,contact 38, contact arm 29, bimetallic element 21, conductors 63 and'64, contact 24, switch blade 28, conduc-,

tors 65 and 58, heating element 39, conductor 59, contact 42, switchblade 4|, conductor 68, relay coil |1, conductor 6|, switch blades 31and 36, and conductor 62 to the other terminal of secondary 52. It willbe noted that the circuit just traced is independent of contact 3|. Itis now possible for the contact blade 29 to move away from contact 3|without interrupting the energization of the relay coil. The relay coilthus does not become deenergized until contact arm 29 disengages contact38. It will thus be seen that a differential is required betweenenergization and deenergization of the relay |6, thus eliminating anydanger of excessively frequent energization and deenergization of thecontrol apparatus by reason of a chattering of the thermostat contacts.

The moving of relay switch blade 2| into engagement with contact 25results in the establishment of the following energizing circuit to theoil burner motor l2: from line wire 53, through conductor 66, contact25, switch blade 2|, conductors 61 and 68, burner motor l2, andconductor 69 to the other line wire 54. At the same time the followingcircuit is established to the ignition means l4: from line wire 53through conductor 66, contact 25,v switch blade 2|, conductors 61 and1|, ignition means I 4, and conductors 12 and 69 to the other line wire54. The establishment of these two circuits to the oil burner motor andto the ignition means results in the establishment of the conditionsnecessary for combustion.

It will be noted that the two circuits traced to relay coil |1 includedheating element 39. If combustion does not take place within apredetermined period of time after the ignition of the oil burner motorand the ignition means l4, the heating element 39 will heat thebimetallic element 38 sufliciently that it will permit switch blade 31to drop away from switch blade 36. When this happens, the completesystem is deenergized and cannot be reenergized until the safety switch35 is manually reclosed by the operator.

If combustion does take place upon energiza- ,tion of the oil burner mor and the ignition means l4, as will usually be the case, thetemperature of the stack will very quickly rise so as to cause switchblade 4| to move first into engagement with contact 43 and immediatelythereafter out of engagement with contact 42.

As soon as switch blade 4| engages contact 43, a new circuit isestablished to the relay coil I! as follows: from the right-handterminal of secondary 52 through conductor 56, contact 38, contact arm29, bimetallic element 21, conductors 63 and 13, contact 23, switchblade I9, conductor I4, choke coil 45, conductor I5, contact 43, switchblade 4|, conductor 68, relay coil I1, conductor 6|, switch blades 31and 36, and conductor 62 to the other treminal of relay coil 52. It willbe noted that this new circuit includes the choke coil 45. Until theswitch blade 4| disengages contact 42, however, the choke coil 45 iseffectively shunted out of the circuit since the resistance of heater 39is relatively small. As soon as switch blade 4| leaves contact 42, thisshunt circuit through heater 39 is interrupted and all of the current torelay coil I! must pass through the choke coil 45. It will be seen thatthe stack switch 48 has had two effects. In the first place, it hasconnected the choke coil 45 in series with relay I! to thereby reducethe drop in voltage necessary to cause the relay to move to itsdeenergized position. In the second place, the heating coil 39 has beendeenergized to thereby render the safety switch 35 inoperative tointerrupt operation of the system. This deenergization of the heatingelement 39 is desirable since it is now assured that combustion has beenestablished.

By reason of the fact that the choke coil 45 has the same power factoras the relay coil N, there will be no disturbance in the power factor ofthe circuit when the choke coil isconnected in series with the relaycoil. It is true that the resistance of heating element 39 is removedfrom the circuit but this resistance is so slight that it does notappreciably affect the power factor of the circuit. Since the powerfactor of the circuit is not changed, the relay coil I! will not dropout, even momentarily.

It is further to be noted that the circuit for the relay coil I'Iincluding the choke coil 45 is dependent upon the closure of the switchblade I9 with contact 23. Thus if the voltage should drop, causing therelay IE to move to its deenergized position, the relay could not againbe reenergized until the stack temperature had cooled down suflicientlyto remake switch blade 4| with contact 42 to reestablish the originalenergizing circuit for the relay. If some such means as this were notprovided, the relay might drop out upon the choke coil being connectedin series therewith merely as a result of the heavy load placed on theline by both the oil burner motor and ignition means, and then wouldimmediately pull in again as soon as the oil burner and ignition wasdisconnected by reason of the relay dropping out. The relay would thuscycle back and forth between its energized and deenergized positions.With the present arrangement, it is assured that when the relay dropsout, it must stay out until the stack has cooled down sulficiently toreengage switch blade 4| with contact 42.

With the choke coil 45 connected in series with relay coil I1, anyappreciable drop in voltage will be effective to cause an immediatemovement of relay I6 to its deenergized position. As soon as the relaymoves from its energized position, the energizing circuit thereto iscompletely broken and the system is not restarted until both the voltageis restored to normal and the stack switch has moved back to its coldposition. If the stack switch moves back to its cold position and thevoltage is still too low, the heating element 39 will eventually heat upand cause safety switch 35 to deenergize the system.

If flame failure occurs for any reason during operation of the system,the cooling of the stack temperature will cause switch blade 4| toreengage contact 42. Relay I'I will once more be energized, if .contactblade 29 is still in engagement with contact 3| whereupon the entirecycle will be repeated. Thus upon flame failure during operation, it ispossible to again automatically restart the burner if conditions areproper. If not, the safety switch 35 is opened just as during the normalstarting period.

Species of Figure 2 In certain types of systems, it will be desirable tohave the choke coil connected in series with the relay coil immediatelyupon energization of the relay coil. Such a relay circuit is shown inFigure 2. In this figure, the relay is designated by the referencenumeral 88 and comprises a relay coil 8| which has associated therewitha movable armature 82 adapted to position switch blades 83 and 84. Theswitch blades 83 and 84 are biased to the right, switch blade 83 beingbiased into engagement with a contact 85. Switch blade 84 is adapted tobe moved into engagement with a contact 86. Upon energization of therelay coil 8|, switch blade 83 is moved out of engagement with contact85 and switch blade 84 into engagement with contact 86. The switch blade84 and contact 86 may be used to control any suitable load circuit. Athermostat 8! is shown as controlling the energization of the relay 88.This thermostat comprises a bimetallic element 88 and a contact arm 89secured thereto. The contact arm 89 is adapted to move into engagementwith a fixed contact 98 upon a suflicient temperature drop. A magnet 9|is associated with the contact arm 89 to impart a snap action thereto.

A step-down transformer is generally indicated by the reference numeral93. This transformer comprises a line voltage primary 84 and a lowvoltage secondary 95. This transformer corresponds to the transformer 58of the species of Figure 1. A choke coil 96 corresponds to the chokecoil This choke coil, like choke coil 45, comprises a winding 91 and amagnetic core 98.

When the temperature to which thermostat 81 is subjected drops to apredetermined point, contact arm 89 is moved into engagement withcontact 98 with a snap action. Upon this occurring, the relay coil 8| isenergized through the following circuit: from the right-hand terminal ofsecondary 95 through conductor I88, contact 98, contact arm 89,bimetallic element 88, conductors I8| and I82, switch blade 83, contact85, conductor I83, relay coil 8 I and conductor I84 to the otherterminal of secondary 95.. In addition to the energizing circuit justmentioned, there is also a circuit established to relay coil 8| asfollows: from the right-hand terminal of secondary 95 through conductorI88, contact 98, contact arm 89, bimetallic element 88, conductors I8Iand I86, choke coil 96, conductor I81, relay coil 8|, and conductor I84to the other terminal of secondary 95. Inasmuch as the choke coil 96 iseffectively shunted by conductor I82, switch blade 83, contact 85, andconductor I83, this second circuit will play no particular part in theenergization of relay coil 8| so long as switch blade 83 is inengagement with contact 85. Upon energization of the relay coil 8|,however, switch blade 83 is moved out of engagement with contact 85,thus interrupting the shunt around choke coil 96 so that choke coil 96is now effectively connected in series with relay coil M.

The connection of choke coil 96 in series with relay coil 8| has thesame effect as the connection of choke coil 45 in series with the relayin the species of Figure 1. In other words, upon any appreciabledrop inthe supply voltage, the relay 8!] moves to its deenergized position. Asin the preferred species, the power factor of the choke coil 96 is thesame as that of the relay 8| when the armature is in its energizedposition. Thus, the connection of the choke coil 96 in series with therelay 8| does not disturb even momentarily the power factor of theentire relay circuit.

It will be seen that I have provided a new and I novel relay circuit inwhich the drop-out voltage of the relay is increased without disturbingthe power factor of the relay circuit. While I have disclosed a specificembodiment of my invention for piu'poses of illustration, it is to beunderstood that the invention is to be limited only by the scope of theappended claims.

I claim as my invention:

In combination, a device biased to one positionand including anelectromagnetic operator for moving it to another position, analternating current source of power for energizing said electromagneticoperator, a constant impedance having the same power factor as saidoperator when said device is in said other position, and means operativesubsequent to the energization of said operator to connect saidimpedance in series with said operator so as to reduce the drop involtage necessary to cause said device to return to its biased position.

2. In combination, an electromagnetic relay, an alternating currentsource of power for energizing said relay, a constant impedance havingthe same power factor as said relay when in its energized position, andmeans operative subsequent to the energization of said relay to connectsaid impedance in series with said relay.

3. In combination, an electromagnetic relay biased to one position andadapted upon energization to move to a second position, an alternatingcurrent source of power for energizing said relay, a constant impedancehaving the same power factor as said relay when in said second position,and means operative subsequent to the energization of said relay toconnect said impedance in series with said relay so as to reduce thedrop in voltage necessary to cause said relay to return to its biasedposition.

4. In combination, a device biased to one position and including anelectromagnetic operator for moving it to another position, analternating current source of power for energizing said electromagneticoperator, a constant impedance choke coil having the same power factoras said operator when said device is in said other position, and meansoperative subsequent to the energization of said operator to connectsaid choke coil in series with said operator so as to reduce the drop involtage necessary to cause said device to return to its biased position.

5. In combination, an electromagnetic relay, an alternating currentsource of power for energizing said relay, a constant impedance chokecoil having the same power factor as said relay when in its energizedposition, and means operative subsequent to the energization of saidrelay to connect said choke coil in series with said relay.

6. In combination, an electrically operated condition producing device,a relay comprising an; electromagnetic coil and a plurality of switchesactuated thereby, one ofsaid switches controlling the energization ofsaid device, a switch controlling the energization of said coll, aconstant impedance having the same power factor as said relay coil whensaid switches are in their energized position, and means dependent uponboth the movement of one of said relay switches to its energizedposition and the'establishment of the condition produced by energizationof said device for connecting said impedance in series with said coil.

7. In combination, an electrically operated condition producing device,a relay comprising an electromagnetic coil and a plurality of switchesactuated thereby, one of said switches controlling the energiz-ation ofsaid device, a switch controlling the energizationn of said coil, aconstant impedance having the same power factor as said relay coil whensaid switches are in their energized position, and means dependent uponboth the movement of one of said relay switches to its energizedposition and the establishment of the condition produced by energizationof said device for establishing a new energizing circuit for the relaycoil including said impedance and for interrupting the initialenergizing circuit for the coil.

8. In combination, a device biased to one position and including anelectromagnetic operator for moving it to another position, analternating current source of power for energizing said electromagneticoperator, a constant impedance having the same power factor as saidoperator when said device is in said other position, said impedancebeing connected in series with said operator, means for normallyshunting said impedance, and means operative subsequent to theenergization of said operator to interrupt said shunting means.

9. In combination, an electromagnetic relay, an alternating currentsource of power for energizing said relay, a constant impedance havingthe same power factor as said relay when energized and connected inseries therewith, means for normally shunting said impedance, and meansoperative subsequent to the energization of said operator to interruptsaid shunting means.

10. In combination, an electromagnetic relay biased to one position andadapted upon energization to move to a second position, an alternatingcurrent source of power for energizing said relay, a constant impedancehaving the same power factor as said relay when energized and connectedin series therewith, means for normally shunting said impedance, andmeans operative subsequent to the energization of said operator tointerrupt said shunting means and thereby reduce the drop in voltagenecessary to cause said relay to return to its biased position.

JOHN M. WILSON.

